Although it can in principle be applied to any desired integrated circuits, the present invention and the problems on which is based are explained with reference to chips with integrated circuits using silicon technology.
Customary solutions for connecting an integrated circuit to a substrate are the use of solder balls of ball-grid arrays for the mechanical connection and the additional use of an underfilling, in order to increase the stability. The underfilling usually consists of an epoxy resin which is filled into the gap between the chip and the substrate. The underfilling serves for increasing the adhesion of the chip on the substrate and for increasing the stability in the x, y and z directions. A further function of the underfilling is to reduce the stresses which occur during temperature changes, and are caused by the thermal mismatch of the chip material and the substrate material.
However, it has been found to be disadvantageous with the customary solutions that the connection by the solder balls between the chip and the substrate has inadequate mechanical stability. Therefore, an underfilling is additionally used to increase the mechanical stability of the system. The introduction of the underfilling material is usually carried out at module level, to be precise after the reflow soldering of the components.
This underfilling process has the following disadvantages.
It is a serial process, in which a drop of the underfilling material has to be placed onto the edges of each individual soldered chip. It is not possible to make the process a parallel process. Moreover, the process is a slow process, since the application of each individual drop of underfilling material requires considerable time. The process cannot be reproduced very well, since bubbles and voids often remain between the chip and the substrate. Furthermore, it does not make it possible to produce delimited adhesion regions and regions which are free from underfilling material. Finally, the process is not suitable for repairing mounted circuit arrangements.
As a result of the disadvantages mentioned above, the process costs are high and the process is complex.